The invention relates to a cannula and a screw pump for use in a mechanical circulatory support device in particular a transventricular circulatory support device. The invention also relates to a method of providing mechanical transventricular support in open and closed chest approaches using said cannula and/or said screw pump.
In the course of coronary artery bypass grafting (CABG) without the use of the classical heart-lung machine, it may be required to provide a mechanical circulatory support system to boost failing heart performance. During bypass grafting on the beating heart, occlusion of segments of coronary arteries can cause failure of the pump function of both heart chambers due to lack of oxygen in the heart muscle or due to arrhytmia. Displacing of the beating heart within the thorax to obtain access to the coronary anastomotic site of the heart, may also lead to mechanical interference with the pump function. This may require the temporary use of an auxiliary blood pump. Such a blood pump may be placed outside or inside the blood circulation. The right and left heart chambers form two pumps placed in series, which may each be assisted in their pump function by a right ventricle assist device (RVAD) and left ventricle assist device (LVAD), respectively.
For a right ventricle assist device (RVAD), the pump outside the circulation bypasses the blood flow that enters the right atrium and that passes from the right atrium via the right ventricle into the pulmonary trunc. Placement of the pump outside the circulation leads to two holes in the circulatory system, one access hole for the cannula that supplies blood from the venous side of the systemic circulation to the assist pump and a second access hole for the output cannula of the assist pump. The inflow cannula of the assist pump may be put in place via a stab wound in the right atrium or right ventricle wall, or via a puncture in a large systemic vein, such as the jugular or femoral vein. The outflow cannula of the assist pump can be placed distal to the right ventricular outflow valves e.g via a puncture hole in the pulmonary trunc. For a LVAD, the bypass connects the left atrium or left ventricle to the aorta, or may comprise an apical cannulation.
Different types of extra-corporeally placed assist pumps may be used, such as a DeBakey roller pump, continuous flow pumps such as centrifugal pumps and rotary blood pumps, pulsatile pumps, etc.
When the assist pump is used within the circulation, only a single access site is needed. An axial catheter-mounted screw pump, marketed by Johnson and Johnson of Warren, N.J. under the trade name HEMOPUMP, utilises a principle similar to that of an Archimedes screw. When used for left ventricle support, the screw element, which is placed inside a curved silicone rubber catheter, is positioned in the aorta, with the inlet in the left ventricle lumen. The pump assembly is made of stainless steel and has about the size of a pencil. The drive motor of the screw element is located extracorporeally, and drives the screw element at about 25000 rpm such that the pump draws a steady stream from the left ventricle. For right ventricle support, the pump can be inserted in the pulmonary artery through a stab wound, the inlet side being positioned in the lumen of the right ventricle.
The above methods of cannulation for the intra and extracorporeally placed assist pumps have several disadvantages. Firstly, access to the circulation is achieved through a cut in possibly calcified vessels. Secondly, the methods may result in dislodgement of plaque with consequent risk of embolisation. Thirdly, false air aspiration may occur at the cannulation site for blood withdrawal, with subsequent risk of air embolisation. Finally, in case a so-called xe2x80x9creverse hemopumpxe2x80x9d is used which is introduced into the circulation via one of the ventricles, or during cannulation of the apex of the left ventricle for a LVAD, a cut into the heart muscle may lead to bleeding complications.
It is therefore an object of the present invention to provide a cannula, a pump, and method of using the same in right or left transventricular mechanical support, which avoid the above drawbacks, and which allow for rapid placement through the least vulnerable tissues without the need of a cut in diseased blood vessels, such as a calcified ascending aorta or stenosed calcified peripheral arteries. It is a further object of the present invention to provide a cannula, pump and method of transventricular mechanical circulatory support in which cannulation of the large outflow vessels of the right and left ventricle (pulmonary trunc or artery and aorta, respectively) need not be cannulated, and which can be carried out in a minimally invasive manner, preferably under close chest conditions.
Hereto the cannula according to the present invention comprises a tubular member made of a flexible, collapsible material having a diameter between 0.5 cm and 3 cm, preferably between 1 cm and 2.5 cm. Preferably the material of the cannula is substantially non-extendible. When used as a RVAD, the cannula according to the present invention can be introduced into the right atrium via a cut into a larger vein, whereafter the distal end is introduced into the right ventricle via the tricuspid valve. The sharply curved trajectory at the apex of the right ventricle can be easily followed by the very flexible cannula of the present invention. From the right ventricle the flexible cannula is guided along the right ventricle outflow valve and is lodged with its distal (outflow) end in the pulmonary artery or pulmonary trunc. The inflow side of the cannula may be connected to an extra or intracorporeally situated bloodpump. The very flexible cannula, which upon insertion is collapsed to very small dimensions, may be inserted directly into the atrium during open or closed chest CABG or may be inserted in a peripheral vein (e.g. femoral or jugular or axillar vein) and advanced to a central location for blood delivery in the pulmonary artery. The assist pump may remain outside the chest. A similar procedure applies to the use of the cannula of the present invention for left ventricle assist devices (LVAD). A LVAD may form a bypass for drainage of blood from the left atrium and for blood delivery to the aorta. The flexible cannula may be introduced into the left atrium through the right upper pulmonary vein, or right atrium with subsequent perforation of the atrial septum, or via the left atrial roof or left atrial appendage.
A suitable material for the cannula comprises polymer (polyethane) angioplastic balloon material or polyurethane with a wall thickness of between 100 and 300 micrometer. Such material can easily drape and flex without being extendible, such that it can be collapsed to very small dimensions to be easily manipulated within the heart.
In a preferred embodiment the cannula comprises a first lumen of a relatively large diameter and a second lumen parallel to the first lumen, and of a smaller diameter. The second lumen may be formed by lengthwise sealing together opposite located walls of the flexible cannula. A flexible guiding catheter may be introduced in the smaller lumen for guiding the flexible cannula to its proper position and for serving as a guideline that provides shape stability to the flexible cannula in the axial direction. The end of the flexible cannula may comprise a guide element of relatively short length such as a rail runner, for receiving a guide wire therethrough. The guide element may comprise an internal thread such that the cannula may be transported by rotation of the threaded guide wire which propels the guide element.
In one embodiment, the flexible cannula comprises a balloon at or near the distal portion of the cannula which allows vacuum collapse of the proximal and mid portion of the cannula upon introduction. This prevents filling of the lumen of the cannula and subsequently volume trapping. When the cannula is placed in its proper position, the guide catheter and the balloon may be withdrawn from the vessel or, alternatively, the catheter may be left in place to serve as a backbone for providing longitudinal dimensional stability to the flexible cannula. The second lumen of the cannula surrounding the backbone catheter avoids stagnant flow areas and prevents direct blood contact with less biocompatible components of the catheter wire.
For attachment of the inflow side of the flexible cannula to a regular rigid cannula or to an intracorporeally located screw pump, the cannula may at its proximal end comprise a ring-shaped inflatable element which is provided with an inflation lumen. Upon inflation of the ring-shaped element, the proximal end of the flexible cannula is clampingly engaged with the rigid inflow cannula or with a screw pump attachment part.
Even though the flexible cannula according to the present invention may be used with a pump which is placed either inside or outside the blood circulation, it is preferred that it is used together with an Archimedes type screw pump having a flexible central drive shaft and an inflatable body having a free edge defining a spiral-shaped contour around the central drive shaft and an inner edge connected to the drive shaft. The inflatable Archimedes type screw pump may be attached to the inlet side of the cannula while its rotary drive shaft extends to outside the body where it is rotated by a motor drive unit This yields a completely transluminal ventricular assist system with an acceptable small diameter upon introduction and retrieval from a peripheral vessel and having a sufficiently large diameter after expansion of the inflatable Archimedes type screw pump and the flexible cannula to deliver a blood flow at a rate of 2 liters per minute or more.
For RVAD blood delivery to the pulmonary trunc the inflatable Archimedes type screw pump may be inserted through the peripheral access through femoral, jugular or axillar vein, or transthoracally through a key hole access directly into the right atrium. For LVAD, (blood delivery to the ascending aorta), the right upper pulmonary vein, or the atrial appendage or the roof of the left atrium or the left ventricular apex may be stabbed directly in the open chest or closed chest approach. Alternatively, for LVAD, access to the left heart side may be reached from the venous circulation using the latter access and by subsequently perforating the wall (atrial septum) between the right and left atrium.